The present invention relates to a concentrating solar collector wherein the reflected rays are concentrated on a small area (hereinafter called "point focusing solar collector").
There exist many kinds of solar collectors. They may be divided generally into two types:
1. Those achieving temperatures upto 100.degree. C. which are used in particular to obtain hot water for domestic purposes. For this purpose there exist many collectors, mainly static, flat ones which are quite cheap. However, these known solar collectors are not satisfactory for industry as one cannot achieve temperatures of more than 100.degree. C. which temperature is required for many industrial purposes, e.g. for obtaining steam.
2. Concentrating collectors which achieve temperatures higher than 100.degree. C., which collectors advantageously trace the position of the sun. The concentration may be achieved with the aid of lenses, which, however are rather combersome, complicated and expensive. The concentration may also be achieved by way of reflecting surfaces. The collectors comprising such reflecting surfaces may be constructed in one of the following manners:
a. a linear concentrating solar collector comprising channels having a parabolic cross-section which channels. serve as reflecting surfaces; and a linear absorber being located at the linear focus of the collector. Such a collector is described and claimed in co-pending Israel Patent Application No. 65238.
b. a point focusing collector comprising reflecting surfaces giving a paraboidal surface and an absorber being located at the focus of the paraboloid. PA1 a. a central construction being the skeleton; PA1 b. at least one pair of segments bearing reflecting surfaces, said segments being built in such a manner that they approximate a paraboloidal surface, said segments being arranged in a symmetrical manner on both sides of the vertical axis of the collector; each segment comprising: PA1 c. means for connecting the segments to the central construction; PA1 d. means for connecting the segments to each other; PA1 e. a stand for bearing the segments being provided with means for rotating the same in the vertical and/or horizontal direction for tracing the position of the sun; and PA1 f. an absorber located at the focus of the collector and being mounted on the central construction.
It is readily understood that in a point focusing solar collector a higher concentration of rays can be achieved than in a linear concentrating solar collector. As a result of this higher concentration higher temperatures and a better efficiacy should be achieved.
However, so far no commercially successful point focusing solar collector has been built. There exist severe technical difficulties in the manufacture of the paraboloidal reflecting surface. Said surface should be precise, have a high optical qualtity and be constantly stable. Moreover, it is rather difficult to manufacture such a collector and to assemble it. The maintenance and the operation of such collectors is cumbersome and complicated and the price thereof is too high.
It has therefore been desirable to devise a point focusing collector which overcomes the above drawbacks, i.e. one which gives high working temperatures and a rather high efficiency. Moreover, all parts thereof should be easy to manufacture and to transport and it should also be easy to assemble the collector. Said collector should be relatively cheap and the reflecting surfaces should be of high optical quality, stable and easy to adjust.